<?php

/**
 * @file
 * API functions for processing and sending e-mail.
 */

/**
 * Auto-detect appropriate line endings for e-mails.
 *
 * $conf['mail_line_endings'] will override this setting.
 */
define('MAIL_LINE_ENDINGS', isset($_SERVER['WINDIR']) || strpos($_SERVER['SERVER_SOFTWARE'], 'Win32') !== FALSE ? "\r\n" : "\n");

/**
 * Compose and optionally send an e-mail message.
 *
 * Sending an e-mail works with defining an e-mail template (subject, text
 * and possibly e-mail headers) and the replacement values to use in the
 * appropriate places in the template. Processed e-mail templates are
 * requested from hook_mail() from the module sending the e-mail. Any module
 * can modify the composed e-mail message array using hook_mail_alter().
 * Finally drupal_mail_system()->mail() sends the e-mail, which can
 * be reused if the exact same composed e-mail is to be sent to multiple
 * recipients.
 *
 * Finding out what language to send the e-mail with needs some consideration.
 * If you send e-mail to a user, her preferred language should be fine, so
 * use user_preferred_language(). If you send email based on form values
 * filled on the page, there are two additional choices if you are not
 * sending the e-mail to a user on the site. You can either use the language
 * used to generate the page ($language global variable) or the site default
 * language. See language_default(). The former is good if sending e-mail to
 * the person filling the form, the later is good if you send e-mail to an
 * address previously set up (like contact addresses in a contact form).
 *
 * Taking care of always using the proper language is even more important
 * when sending e-mails in a row to multiple users. Hook_mail() abstracts
 * whether the mail text comes from an administrator setting or is
 * static in the source code. It should also deal with common mail tokens,
 * only receiving $params which are unique to the actual e-mail at hand.
 *
 * An example:
 *
 * @code
 *   function example_notify($accounts) {
 *     foreach ($accounts as $account) {
 *       $params['account'] = $account;
 *       // example_mail() will be called based on the first drupal_mail() parameter.
 *       drupal_mail('example', 'notice', $account->mail, user_preferred_language($account), $params);
 *     }
 *   }
 *
 *   function example_mail($key, &$message, $params) {
 *     $data['user'] = $params['account'];
 *     $options['language'] = $message['language'];
 *     user_mail_tokens($variables, $data, $options);
 *     switch($key) {
 *       case 'notice':
 *         // If the recipient can receive such notices by instant-message, do
 	*         // not send by email.
 *         if (example_im_send($key, $message, $params)) {
 *           $message['send'] = FALSE;
 *           break;
 *         }
 *         $langcode = $message['language']->language;
 *         $message['subject'] = t('Notification from !site', $variables, array('langcode' => $langcode));
 *         $message['body'][] = t("Dear !username\n\nThere is new content available on the site.", $variables, array('langcode' => $langcode));
 *         break;
 *     }
 *   }
 * @endcode
 *
 * Another example, which uses drupal_mail() to format a message for sending
 * later:
 *
 * @code
 *   $params = array('current_conditions' => $data);
 *   $to = 'user@example.com';
 *   $message = drupal_mail('example', 'notice', $to, $language, $params, FALSE);
 *   // Only add to the spool if sending was not canceled.
 *   if ($message['send']) {
 *     example_spool_message($message);
 *   }
 * @endcode
 *
 * @param $module
 *   A module name to invoke hook_mail() on. The {$module}_mail() hook will be
 *   called to complete the $message structure which will already contain common
 *   defaults.
 * @param $key
 *   A key to identify the e-mail sent. The final e-mail id for e-mail altering
 *   will be {$module}_{$key}.
 * @param $to
 *   The e-mail address or addresses where the message will be sent to. The
 *   formatting of this string must comply with RFC 2822. Some examples are:
 *   - user@example.com
 *   - user@example.com, anotheruser@example.com
 *   - User <user@example.com>
 *   - User <user@example.com>, Another User <anotheruser@example.com>
 * @param $language
 *   Language object to use to compose the e-mail.
 * @param $params
 *   Optional parameters to build the e-mail.
 * @param $from
 *   Sets From to this value, if given.
 * @param $send
 *   If TRUE, drupal_mail() will call drupal_mail_system()->mail() to deliver
 *   the message, and store the result in $message['result']. Modules
 *   implementing hook_mail_alter() may cancel sending by setting
 *   $message['send'] to FALSE.
 *
 * @return
 *   The $message array structure containing all details of the
 *   message. If already sent ($send = TRUE), then the 'result' element
 *   will contain the success indicator of the e-mail, failure being already
 *   written to the watchdog. (Success means nothing more than the message being
 *   accepted at php-level, which still doesn't guarantee it to be delivered.)
 */
function drupal_mail($module, $key, $to, $language, $params = array(), $from = NULL, $send = TRUE) {
	$default_from = variable_get('site_mail', ini_get('sendmail_from'));

	// Bundle up the variables into a structured array for altering.
	$message = array(
			'id'       => $module . '_' . $key,
			'module'   => $module,
			'key'      => $key,
			'to'       => $to,
			'from'     => isset($from) ? $from : $default_from,
			'language' => $language,
			'params'   => $params,
			'send'     => TRUE,
			'subject'  => '',
			'body'     => array()
	);

	// Build the default headers
	$headers = array(
			'MIME-Version'              => '1.0',
			'Content-Type'              => 'text/plain; charset=UTF-8; format=flowed; delsp=yes',
			'Content-Transfer-Encoding' => '8Bit',
			'X-Mailer'                  => 'Drupal'
	);
	if ($default_from) {
		// To prevent e-mail from looking like spam, the addresses in the Sender and
		// Return-Path headers should have a domain authorized to use the originating
		// SMTP server.
		$headers['From'] = $headers['Sender'] = $headers['Return-Path'] = $default_from;
	}
	if ($from) {
		$headers['From'] = $from;
	}
	$message['headers'] = $headers;

	// Build the e-mail (get subject and body, allow additional headers) by
	// invoking hook_mail() on this module. We cannot use module_invoke() as
	// we need to have $message by reference in hook_mail().
	if (function_exists($function = $module . '_mail')) {
		$function($key, $message, $params);
	}

	// Invoke hook_mail_alter() to allow all modules to alter the resulting e-mail.
	drupal_alter('mail', $message);

	// Retrieve the responsible implementation for this message.
	$system = drupal_mail_system($module, $key);

	// Format the message body.
	$message = $system->format($message);

	// Optionally send e-mail.
	if ($send) {
		// The original caller requested sending. Sending was canceled by one or
		// more hook_mail_alter() implementations. We set 'result' to NULL, because
		// FALSE indicates an error in sending.
		if (empty($message['send'])) {
			$message['result'] = NULL;
		}
		// Sending was originally requested and was not canceled.
		else {
			$message['result'] = $system->mail($message);
			// Log errors.
			if (!$message['result']) {
				watchdog('mail', 'Error sending e-mail (from %from to %to).', array('%from' => $message['from'], '%to' => $message['to']), WATCHDOG_ERROR);
				drupal_set_message(t('Unable to send e-mail. Contact the site administrator if the problem persists.'), 'error');
			}
		}
	}

	return $message;
}

/**
 * Returns an object that implements the MailSystemInterface.
 *
 * Allows for one or more custom mail backends to format and send mail messages
 * composed using drupal_mail().
 *
 * An implementation needs to implement the following methods:
 * - format: Allows to preprocess, format, and postprocess a mail
 *   message before it is passed to the sending system. By default, all messages
 *   may contain HTML and are converted to plain-text by the DefaultMailSystem
 *   implementation. For example, an alternative implementation could override
 *   the default implementation and additionally sanitize the HTML for usage in
 *   a MIME-encoded e-mail, but still invoking the DefaultMailSystem
 *   implementation to generate an alternate plain-text version for sending.
 * - mail: Sends a message through a custom mail sending engine.
 *   By default, all messages are sent via PHP's mail() function by the
 *   DefaultMailSystem implementation.
 *
 * The selection of a particular implementation is controlled via the variable
 * 'mail_system', which is a keyed array.  The default implementation
 * is the class whose name is the value of 'default-system' key. A more specific
 * match first to key and then to module will be used in preference to the
 * default. To specificy a different class for all mail sent by one module, set
 * the class name as the value for the key corresponding to the module name. To
 * specificy a class for a particular message sent by one module, set the class
 * name as the value for the array key that is the message id, which is
 * "${module}_${key}".
 *
 * For example to debug all mail sent by the user module by logging it to a
 * file, you might set the variable as something like:
 *
 * @code
 * array(
 *   'default-system' => 'DefaultMailSystem',
 *   'user' => 'DevelMailLog',
 * );
 * @endcode
 *
 * Finally, a different system can be specified for a specific e-mail ID (see
 * the $key param), such as one of the keys used by the contact module:
 *
 * @code
 * array(
 *   'default-system' => 'DefaultMailSystem',
 *   'user' => 'DevelMailLog',
 *   'contact_page_autoreply' => 'DrupalDevNullMailSend',
 * );
 * @endcode
 *
 * Other possible uses for system include a mail-sending class that actually
 * sends (or duplicates) each message to SMS, Twitter, instant message, etc, or
 * a class that queues up a large number of messages for more efficient bulk
 * sending or for sending via a remote gateway so as to reduce the load
 * on the local server.
 *
 * @param $module
 *   The module name which was used by drupal_mail() to invoke hook_mail().
 * @param $key
 *   A key to identify the e-mail sent. The final e-mail ID for the e-mail
 *   alter hook in drupal_mail() would have been {$module}_{$key}.
 *
 * @return MailSystemInterface
 */
function drupal_mail_system($module, $key) {
	$instances = &drupal_static(__FUNCTION__, array());

	$id = $module . '_' . $key;

	$configuration = variable_get('mail_system', array('default-system' => 'DefaultMailSystem'));

	// Look for overrides for the default class, starting from the most specific
	// id, and falling back to the module name.
	if (isset($configuration[$id])) {
		$class = $configuration[$id];
	}
	elseif (isset($configuration[$module])) {
		$class = $configuration[$module];
	}
	else {
		$class = $configuration['default-system'];
	}

	if (empty($instances[$class])) {
		$interfaces = class_implements($class);
		if (isset($interfaces['MailSystemInterface'])) {
			$instances[$class] = new $class();
		}
		else {
			throw new Exception(t('Class %class does not implement interface %interface', array('%class' => $class, '%interface' => 'MailSystemInterface')));
		}
	}
	return $instances[$class];
}

/**
 * An interface for pluggable mail back-ends.
 */
interface MailSystemInterface {
	/**
	 * Format a message composed by drupal_mail() prior sending.
	 *
	 * @param $message
	 *   A message array, as described in hook_mail_alter().
	 *
	 * @return
	 *   The formatted $message.
	 */
	public function format(array $message);

	/**
	 * Send a message composed by drupal_mail().
	 *
	 * @param $message
	 *   Message array with at least the following elements:
	 *   - id: A unique identifier of the e-mail type. Examples: 'contact_user_copy',
	 *     'user_password_reset'.
	 *   - to: The mail address or addresses where the message will be sent to.
	 *     The formatting of this string must comply with RFC 2822. Some examples:
	 *     - user@example.com
	 *     - user@example.com, anotheruser@example.com
	 *     - User <user@example.com>
	 *     - User <user@example.com>, Another User <anotheruser@example.com>
	 *    - subject: Subject of the e-mail to be sent. This must not contain any
	 *      newline characters, or the mail may not be sent properly.
	 *    - body: Message to be sent. Accepts both CRLF and LF line-endings.
	 *      E-mail bodies must be wrapped. You can use drupal_wrap_mail() for
	 *      smart plain text wrapping.
	 *    - headers: Associative array containing all additional mail headers not
	 *      defined by one of the other parameters.  PHP's mail() looks for Cc
	 *      and Bcc headers and sends the mail to addresses in these headers too.
	 *
	 * @return
	 *   TRUE if the mail was successfully accepted for delivery, otherwise FALSE.
	 */
	public function mail(array $message);
}

/**
 * Perform format=flowed soft wrapping for mail (RFC 3676).
 *
 * We use delsp=yes wrapping, but only break non-spaced languages when
 * absolutely necessary to avoid compatibility issues.
 *
 * We deliberately use LF rather than CRLF, see drupal_mail().
 *
 * @param $text
 *   The plain text to process.
 * @param $indent (optional)
 *   A string to indent the text with. Only '>' characters are repeated on
 *   subsequent wrapped lines. Others are replaced by spaces.
 */
function drupal_wrap_mail($text, $indent = '') {
	// Convert CRLF into LF.
	$text = str_replace("\r", '', $text);
	// See if soft-wrapping is allowed.
	$clean_indent = _drupal_html_to_text_clean($indent);
	$soft = strpos($clean_indent, ' ') === FALSE;
	// Check if the string has line breaks.
	if (strpos($text, "\n") !== FALSE) {
		// Remove trailing spaces to make existing breaks hard.
		$text = preg_replace('/ +\n/m', "\n", $text);
		// Wrap each line at the needed width.
		$lines = explode("\n", $text);
		array_walk($lines, '_drupal_wrap_mail_line', array('soft' => $soft, 'length' => strlen($indent)));
		$text = implode("\n", $lines);
	}
	else {
		// Wrap this line.
		_drupal_wrap_mail_line($text, 0, array('soft' => $soft, 'length' => strlen($indent)));
	}
	// Empty lines with nothing but spaces.
	$text = preg_replace('/^ +\n/m', "\n", $text);
	// Space-stuff special lines.
	$text = preg_replace('/^(>| |From)/m', ' $1', $text);
	// Apply indentation. We only include non-'>' indentation on the first line.
	$text = $indent . substr(preg_replace('/^/m', $clean_indent, $text), strlen($indent));

	return $text;
}

/**
 * Transform an HTML string into plain text, preserving the structure of the
 * markup. Useful for preparing the body of a node to be sent by e-mail.
 *
 * The output will be suitable for use as 'format=flowed; delsp=yes' text
 * (RFC 3676) and can be passed directly to drupal_mail() for sending.
 *
 * We deliberately use LF rather than CRLF, see drupal_mail().
 *
 * This function provides suitable alternatives for the following tags:
 * <a> <em> <i> <strong> <b> <br> <p> <blockquote> <ul> <ol> <li> <dl> <dt>
 * <dd> <h1> <h2> <h3> <h4> <h5> <h6> <hr>
 *
 * @param $string
 *   The string to be transformed.
 * @param $allowed_tags (optional)
 *   If supplied, a list of tags that will be transformed. If omitted, all
 *   all supported tags are transformed.
 *
 * @return
 *   The transformed string.
 */
function drupal_html_to_text($string, $allowed_tags = NULL) {
	// Cache list of supported tags.
	static $supported_tags;
	if (empty($supported_tags)) {
		$supported_tags = array('a', 'em', 'i', 'strong', 'b', 'br', 'p', 'blockquote', 'ul', 'ol', 'li', 'dl', 'dt', 'dd', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'hr');
	}

	// Make sure only supported tags are kept.
	$allowed_tags = isset($allowed_tags) ? array_intersect($supported_tags, $allowed_tags) : $supported_tags;

	// Make sure tags, entities and attributes are well-formed and properly nested.
	$string = _filter_htmlcorrector(filter_xss($string, $allowed_tags));

	// Apply inline styles.
	$string = preg_replace('!</?(em|i)((?> +)[^>]*)?>!i', '/', $string);
	$string = preg_replace('!</?(strong|b)((?> +)[^>]*)?>!i', '*', $string);

	// Replace inline <a> tags with the text of link and a footnote.
	// 'See <a href="http://drupal.org">the Drupal site</a>' becomes
	// 'See the Drupal site [1]' with the URL included as a footnote.
	_drupal_html_to_mail_urls(NULL, TRUE);
	$pattern = '@(<a[^>]+?href="([^"]*)"[^>]*?>(.+?)</a>)@i';
	$string = preg_replace_callback($pattern, '_drupal_html_to_mail_urls', $string);
	$urls = _drupal_html_to_mail_urls();
	$footnotes = '';
	if (count($urls)) {
		$footnotes .= "\n";
		for ($i = 0, $max = count($urls); $i < $max; $i++) {
			$footnotes .= '[' . ($i + 1) . '] ' . $urls[$i] . "\n";
		}
	}

	// Split tags from text.
	$split = preg_split('/<([^>]+?)>/', $string, -1, PREG_SPLIT_DELIM_CAPTURE);
	// Note: PHP ensures the array consists of alternating delimiters and literals
	// and begins and ends with a literal (inserting $null as required).

	$tag = FALSE; // Odd/even counter (tag or no tag)
	$casing = NULL; // Case conversion function
	$output = '';
	$indent = array(); // All current indentation string chunks
	$lists = array(); // Array of counters for opened lists
	foreach ($split as $value) {
		$chunk = NULL; // Holds a string ready to be formatted and output.

		// Process HTML tags (but don't output any literally).
		if ($tag) {
			list($tagname) = explode(' ', strtolower($value), 2);
			switch ($tagname) {
				// List counters
				case 'ul':
					array_unshift($lists, '*');
					break;
				case 'ol':
					array_unshift($lists, 1);
					break;
				case '/ul':
				case '/ol':
					array_shift($lists);
					$chunk = ''; // Ensure blank new-line.
					break;

					// Quotation/list markers, non-fancy headers
				case 'blockquote':
					// Format=flowed indentation cannot be mixed with lists.
					$indent[] = count($lists) ? ' "' : '>';
					break;
				case 'li':
					$indent[] = isset($lists[0]) && is_numeric($lists[0]) ? ' ' . $lists[0]++ . ') ' : ' * ';
					break;
				case 'dd':
					$indent[] = '    ';
					break;
				case 'h3':
					$indent[] = '.... ';
					break;
				case 'h4':
					$indent[] = '.. ';
					break;
				case '/blockquote':
					if (count($lists)) {
						// Append closing quote for inline quotes (immediately).
						$output = rtrim($output, "> \n") . "\"\n";
						$chunk = ''; // Ensure blank new-line.
					}
					// Fall-through
				case '/li':
				case '/dd':
					array_pop($indent);
					break;
				case '/h3':
				case '/h4':
					array_pop($indent);
				case '/h5':
				case '/h6':
					$chunk = ''; // Ensure blank new-line.
					break;

					// Fancy headers
				case 'h1':
					$indent[] = '======== ';
					$casing = 'drupal_strtoupper';
					break;
				case 'h2':
					$indent[] = '-------- ';
					$casing = 'drupal_strtoupper';
					break;
				case '/h1':
				case '/h2':
					$casing = NULL;
					// Pad the line with dashes.
					$output = _drupal_html_to_text_pad($output, ($tagname == '/h1') ? '=' : '-', ' ');
					array_pop($indent);
					$chunk = ''; // Ensure blank new-line.
					break;

					// Horizontal rulers
				case 'hr':
					// Insert immediately.
					$output .= drupal_wrap_mail('', implode('', $indent)) . "\n";
					$output = _drupal_html_to_text_pad($output, '-');
					break;

					// Paragraphs and definition lists
				case '/p':
				case '/dl':
					$chunk = ''; // Ensure blank new-line.
					break;
			}
		}
		// Process blocks of text.
		else {
			// Convert inline HTML text to plain text; not removing line-breaks or
			// white-space, since that breaks newlines when sanitizing plain-text.
			$value = trim(decode_entities($value));
			if (drupal_strlen($value)) {
				$chunk = $value;
			}
		}

		// See if there is something waiting to be output.
		if (isset($chunk)) {
			// Apply any necessary case conversion.
			if (isset($casing)) {
				$chunk = $casing($chunk);
			}
			// Format it and apply the current indentation.
			$output .= drupal_wrap_mail($chunk, implode('', $indent)) . MAIL_LINE_ENDINGS;
			// Remove non-quotation markers from indentation.
			$indent = array_map('_drupal_html_to_text_clean', $indent);
		}

		$tag = !$tag;
	}

	return $output . $footnotes;
}

/**
 * Helper function for array_walk in drupal_wrap_mail().
 *
 * Wraps words on a single line.
 */
function _drupal_wrap_mail_line(&$line, $key, $values) {
	// Use soft-breaks only for purely quoted or unindented text.
	$line = wordwrap($line, 77 - $values['length'], $values['soft'] ? "  \n" : "\n");
	// Break really long words at the maximum width allowed.
	$line = wordwrap($line, 996 - $values['length'], $values['soft'] ? " \n" : "\n");
}

/**
 * Helper function for drupal_html_to_text().
 *
 * Keeps track of URLs and replaces them with placeholder tokens.
 */
function _drupal_html_to_mail_urls($match = NULL, $reset = FALSE) {
	global $base_url, $base_path;
	static $urls = array(), $regexp;

	if ($reset) {
		// Reset internal URL list.
		$urls = array();
	}
	else {
		if (empty($regexp)) {
			$regexp = '@^' . preg_quote($base_path, '@') . '@';
		}
		if ($match) {
			list(, , $url, $label) = $match;
			// Ensure all URLs are absolute.
			$urls[] = strpos($url, '://') ? $url : preg_replace($regexp, $base_url . '/', $url);
			return $label . ' [' . count($urls) . ']';
		}
	}
	return $urls;
}

/**
 * Helper function for drupal_wrap_mail() and drupal_html_to_text().
 *
 * Replace all non-quotation markers from a given piece of indentation with spaces.
 */
function _drupal_html_to_text_clean($indent) {
	return preg_replace('/[^>]/', ' ', $indent);
}

/**
 * Helper function for drupal_html_to_text().
 *
 * Pad the last line with the given character.
 */
function _drupal_html_to_text_pad($text, $pad, $prefix = '') {
	// Remove last line break.
	$text = substr($text, 0, -1);
	// Calculate needed padding space and add it.
	if (($p = strrpos($text, "\n")) === FALSE) {
		$p = -1;
	}
	$n = max(0, 79 - (strlen($text) - $p) - strlen($prefix));
	// Add prefix and padding, and restore linebreak.
	return $text . $prefix . str_repeat($pad, $n) . "\n";
}
